Dual gold photoredox C(sp(2))-C(sp(2)) cross couplings - development and mechanistic studies.

A dual visible light photoredox and gold-catalysed C(sp(2))-C(sp(2)) cross coupling is described. The success of this mild, oxidant- and base-free cross coupling is highly dependent on the amount of water added. Mechanistic studies show two distinct pathways depending on the gold catalyst employed: transmetallation of the arylboronic acid with gold(i) occurs prior to oxidation of gold(i) to gold(iii) using cationic gold(i) catalysts, whereas oxidation of gold(i) to gold(iii) precedes transmetallation using neutral gold(i) catalysts.